diff --git a/ChangeLog b/ChangeLog
index e84a35525..34e80d586 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -4,6 +4,8 @@ PolarSSL ChangeLog
 Bug fixes
    * Fixed incorrect handling of negative strings in
      mpi_read_string() (found by code coverage tests).
+   * Fixed incorrect handling of one single negative input
+     value in mpi_add_abs() (found by code coverage tests).
 
 = Version 0.11.1 released on 2009-05-17
    * Fixed missing functionality for SHA-224, SHA-256, SHA384,
diff --git a/library/bignum.c b/library/bignum.c
index 5c1de684c..218e50b5d 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -683,6 +683,11 @@ int mpi_add_abs( mpi *X, mpi *A, mpi *B )
 
     if( X != A )
         MPI_CHK( mpi_copy( X, A ) );
+   
+    /*
+     * X should always be positive as a result of unsigned additions.
+     */
+    X->s = 1;
 
     for( j = B->n - 1; j >= 0; j-- )
         if( B->p[j] != 0 )